Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover the safety profile (readOnly, idempotent, closed-world), so the bar is lower, and the description adds real behavioral detail: both endpoints are counted, a reversed range returns 0, and the maximum supported span is 3,660 days. It stops short of saying what happens (error vs. clipping) when that limit is exceeded.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences (in each language) with zero padding; the core behavior, the reverse-range rule, and the size limit are all front-loaded and easy to scan.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description reasonably implies the return value is a day count and explicitly handles the degenerate reversed-range case. For a read-only counting tool this is nearly complete, though it could clarify error behavior for over-limit ranges.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all five parameters including the calendar enum and the extra_holidays/extra_business_days arrays are already documented in the schema. The description adds no additional meaning about parameter interactions (e.g., precedence between extra_holidays and extra_business_days), so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (count) and resource (business days between start and end), with inclusive-boundary scope spelled out. This is clearly distinguishable from siblings like add_business_days and check_business_day without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives useful edge-case context (start after end yields 0, max range 3,660 days / ~10 years), which implicitly tells the agent when the tool is valid. However, it never explicitly says when to choose this over check_business_day or add_business_days, leaving routing to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.